Conventionally, as an exhaust gas purification apparatus provided in an exhaust passage of an internal combustion engine, an exhaust gas purification apparatus is developed in which a filter carries a selective reduction-type type NOx catalyst (hereinafter, sometimes also referred to as an “SCR catalyst”) which selectively reduces NOx in exhaust gas (for example, refer to Patent Document 1). The filter collects particulate matter (hereinafter, referred to as “PM”) in the exhaust gas. The SCR catalyst reduces the NOx in the exhaust gas using ammonia (NH3) as a reducing agent. Hereinafter, such a filter carrying an SCR catalyst as described above will be referred to as an “SCRF”. In the exhaust gas purification apparatus described in Patent Document 1, an oxidation catalyst and a urea adding valve for NOx purification are arranged on an upstream side of the SCRF. In this manner, by adopting an SCRF as an exhaust gas purification apparatus, an SCR catalyst can be arranged further upstream in an exhaust passage. As a result, the SCR catalyst is more readily heated by heat, of the exhaust gas, whereby a warm-up performance of the SCR catalyst and a NOx purification rate of the SCR catalyst can be improved.
In addition, a supply valve for supplying a reducing agent for reducing and purifying NOx is also arranged in a configuration in which a filter and an SCR catalyst are individually arranged in an exhaust passage of an internal combustion engine. In both an SCRF and a configuration in which a filter and an SCR catalyst are individually arranged, NOx purification due to a reducing action of ammonia is exhibited as a result of ammonia being adsorbed at a prescribed site of the SCR catalyst. However, in an internal combustion engine, there may be cases where a fuel component is supplied into exhaust gas for the purpose of raising the temperature of the exhaust gas or the like. If the fuel component is adsorbed at the prescribed site of the SCR catalyst while being supplied into exhaust gas, NOx purification by the SCR catalyst can no longer be performed with the same effectiveness. In consideration thereof, a technique is disclosed for removing an adsorbed fuel component by forcibly raising the temperature of an SCR catalyst when the fuel component adsorbed by the SCR catalyst reaches or exceeds a prescribed amount (for example, refer to Patent Document 2).